1. Field of the Invention
The present invention relates to an apparatus for, and a method of, canceling, when there are present an input voice signal supplied through a microphone and which has a first sampling frequency and an output voice signal provided from a speaker and which has a second sampling frequency, an echo component developed based on the speaker output voice signal, from the microphone input voice signal, and also to a voice reproducing apparatus using the echo canceling apparatus and method.
2. Description of the Related Art
The voice-frequency terminals such as a portable telephone incur an echo problem that a sound coming from a speaker of the terminal to a microphone causes an echo which will disturb the user in listening to the voice from the speaker. To solve this problem, there has been proposed an echo canceller adapted to estimate the frequency characteristic of an echo path by an adaptive filter and subtract the estinated echo signal from the microphone input signal. The echo canceller is supplied with two signals, one being an input voice signal supplied from a microphone and subjected to analog/digital (A/D) conversion (will be referred to as xe2x80x9cmicrophone input signalxe2x80x9d hereinafter) and the other being the A/D converted signal which is subjected to digital/analog (D/A) conversion for supply to a speaker (will be referred to as xe2x80x9cspeaker output signalxe2x80x9d hereinafter), and thus the echo canceller outputs a voice from which an echo has been canceled.
On the other hand, there has been proposed a band widening technique for estimating an out-of-band component from a narrow-band signal whose sampling frequency is about 8 kHz and voice frequency is about 300 to 3,400 Hz, and synthesizing a wide-band signal whose sampling frequency is about 16 kHz and voice frequency is about 300 to 6,000 Hz.
However, no echo canceling technique has been established for a system which provides an output signal produced from a microphone input signal of 8 kHz in sampling frequency and whose sampling frequency is higher due to band widening and voice frequency band is also wide. This is because to cancel an echo, it is necessary to subtract, from a microphone input signal, of an echo signal which is estimated to come from a speaker and a sampling signal of the speaker input signal has to be equalized to that of the microphone output signal for the purpose of the subtraction.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an echo canceling apparatus and method capable of canceling an echo component from a microphone input signal even if the latter is different in sampling rate from a speaker output signal.
The present invention has another object to provide a voice reproducing apparatus capable of canceling an echo component from an microphone input signal even if the latter is different in sampling rate from a speaker output signal.
The above object can be attained by providing an echo canceling apparatus adapted to cancel, from a microphone input voice signal having a first sampling frequency, an echo component developed based on a speaker output voice signal having a second sampling frequency, the echo canceling apparatus comprising according to the present invention:
means for converting the second sampling frequency of the speaker output voice signal to the first sampling frequency of the microphone input voice signal;
means for estimating an echo signal coming from the speaker to the microphone, based on the speaker output voice signal whose sampling frequency has been converted by the sampling frequency converting means; and
means for subtracting from the microphone input voice signal the echo signal having been estimated by the echo estimating means.
The above echo canceling apparatus further comprises means for limiting the frequency band of the speaker output voice signal to within a range of frequency band of the microphone input voice signal, wherein the sampling frequency converting means converts the sampling frequency of the speaker output signal having been limited in band by the frequency band limiting means to the first sampling frequency, the echo estimating means estimates the echo signal based on the speaker output voice signal whose sampling frequency has been converted, and the subtracting means subtracts the estimated echo signal from the microphone input voice signal.
Also, when the first sampling frequency of the microphone input voice signal is 1/n (n is an integer) of the second sampling frequency of the speaker output voice signal, the sampling frequency converting means decimates the speaker output voice signal to 1/n in amount.
Also, the echo canceling apparatus cancels an echo developed in a voice reproducing apparatus adapted to increase the frequency bandwidth of a narrow-band voice signal supplied thereto and thus output a wide-band voice signal, and the subtracting means subtracts, from the microphone input voice signal, the estimated echo signal having been estimated by the echo estimating means based on the wide-band voice signal of which the sampling frequency has been converted by the sampling frequency converting means.
Also the above object can be attained by providing an echo canceling apparatus adapted to cancel, when an input voice signal of a first sampling frequency entered from a microphone is converted to an output voice signal of a second sampling frequency which is to be pronounced from an speaker, an echo signal developed based on the speaker output voice signal from the microphone input voice signal of the first sampling frequency, the apparatus comprising according to the present invention:
means for estimating an echo component coming from the speaker to the microphone based on a signal having a frequency equal to the first sampling frequency and which is not to be outputted; and
means for subtracting, from the microphone input voice signal, the echo component having been estimated by the echo estimating means.
Also the above object can be attained by providing an echo canceling apparatus adapted to cancel, from a microphone input voice signal of a first sampling frequency, an echo component developed based on a speaker output voice signal of a second sampling frequency, the apparatus comprising according to the present invention:
means for converting the sampling frequency of the microphone input voice signal to the second sampling frequency; and
means for estimating an echo signal coming from the speaker to the microphone based on the output voice signal; and
means for subtracting the echo signal having been estimated by the echo estimating means from the microphone input voice signal whose frequency has been converted by the frequency converting means.
The above object can be attained by providing an echo canceling method adapted to cancel, from a microphone input voice signal having a first sampling frequency, an echo component developed based on a speaker output voice signal having a second sampling frequency, the method comprising, according to the present invention, the steps of:
converting the second sampling frequency of the speaker output voice signal to the first sampling frequency of the microphone input voice signal;
estimating an echo signal coming from the speaker to the microphone based on the speaker output voice signal whose sampling frequency has been converted by the sampling frequency converting means; and
subtracting from the microphone input voice signal the echo signal having been estimated by the echo estimating means.
The above echo canceling method further comprises the steps of limiting the frequency band of the speaker output voice signal to within a range of frequency band of the microphone input voice signal; converting the sampling frequency of the speaker output signal having been limited in band by the frequency band limiting means to the first sampling frequency; and subtracting from the microphone input voice signal an echo signal having been estimated based on the converted output.
Also, when the first sampling frequency of the microphone input voice signal is 1/n (n is an integer) of the second sampling frequency of the speaker output voice signal, the sampling frequency is converted by decimating the speaker output voice signal to 1/n in amount.
Also, the echo canceling method cancels an echo developed in a voice reproducing apparatus adapted to increase the frequency bandwidth of a narrow-band voice signal supplied thereto and thus output a wide-band voice signal, and subtracts, from the microphone input voice signal, the estimated echo signal having been estinated by the echo estimating means based on the wide-band voice signal whose sampling frequency has been converted.
Also the above object can be attained by providing an echo canceling method adapted to cancel, when an input voice signal of a first sampling frequency entered from a microphone is converted to an output voice signal of a second sampling frequency which is to be pronounced from an speaker, an echo signal developed based on the speaker output voice signal from the microphone input voice signal of the first sampling frequency, the method comprising, according to the present invention, the steps of:
estimating an echo component coming from the speaker to the microphone based on a signal having a frequency equal to the first sampling frequency and which is not to be outputted; and
subtracting, from the microphone input voice signal, the echo component having been estimated by the echo estimating means.
Also the above object can be attained by providing an echo canceling method adapted to cancel, from a microphone input voice signal of a first sampling frequency, an echo component developed based on a speaker output voice signal of a second sampling frequency, the method comprising, according to the present invention, the steps of:
converting the sampling frequency of the microphone input voice signal to the second sampling frequency; and
estimating an echo signal coming from the speaker to the microphone based on the output voice signal; and
subtracting the echo signal having been estimated by the echo estimating means from the microphone input voice signal whose frequency has been converted by the frequency converting means.
Also the above object can be attained by providing a voice reproducing apparatus adapted to convert an input voice signal of a first sampling frequency to an output voice signal of a second sampling frequency and pronounce the output voice signal while processing the input voice signal of the first sampling frequency picked up by a microphone, the apparatus comprising according to the present invention:
means for converting the second sampling frequency of the output voice signal to the first sampling frequency of the microphone input voice signal;
means for estimating an echo component coming from the speaker to the microphone based on the output voice signal whose sampling frequency has been converted by the sampling frequency converting means; and
means for subtracting from the microphone input voice signal the echo component having been estimated by the echo estimating means.
Also the above object can be attained by providing a voice reproducing apparatus adapted to convert an input voice signal of a first sampling frequency to an output voice signal of a second sampling frequency and pronounce the output voice signal while processing the input voice signal of the first sampling frequency picked up by a microphone, the apparatus comprising according to the present invention:
means for estimating an echo component coming from the speaker to the microphone based on a signal having a frequency equal to the first sampling frequency and which is not to be outputted; and
means for subtracting from the microphone input voice signal the echo component having been estimated by the echo estimating means.
Also the object can be attained by providing a voice reproducing apparatus adapted to convert an input voice signal of a first sampling frequency to an output voice signal of a second sampling frequency and pronounce the output voice signal while processing the input voice signal of the first sampling frequency picked up by a microphone, the voice reproducing apparatus comprising according to the present invention:
means for converting the frequency of the microphone input voice signal to the second sampling frequency;
means for estimating an echo component coming from the speaker to the microphone based on the output voice signal;
means for subtracting the echo component having been estimated by the echo estimating means from the microphone input voice signal whose frequency has been converted by the frequency converting means.
According to the present invention, the sampling frequency of the speaker output is converted to that of the microphone input, thereby permitting to use the conventional echo canceller in the present invention.
In this method of sampling frequency conversion, when lowering the sampling, the sampling frequency is down-sampled. Also, the down-sampling may be done after limiting the band of the sampling frequency. Moreover, when the sampling rate is an integral multiple, the microphone input signal may be simply decimated for conversion of the sampling frequency. When the sampling rate is other than an integral multiple, a linear interpolation filter may be used without band limitation.
Also, an intermediate output equal in sampling rate to the microphone input, not the speaker output signal, is used, the sampling frequency is converted to that of the microphone input. In this method, a narrow-band frequency signal equal in sampling frequency to the microphone input is used in the band spreading.
On the contrary, the sampling frequency the speaker output may be converted to the sampling frequency of the microphone input, thereby permitting to use an echo canceller. In this case, up-sampling will be done. By any of the above-mentioned methods, echo can be canceled.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiments of the present invention when taken in conjunction with the accompanying drawings.